Dapsone (diamino-diphenyl sulfone) is an antibacterial most commonly used in combination with rifampicin and clofazimine as multidrug therapy (MDT) for the treatment of Mycobacterium leprae infections (leprosy).
Leprosy is a contagious infectious disease with a chronic course and generally with fatal outcome; it is also known as Hansen's Disease (HD), from the Norwegian physician who first isolated the pathogen in Mycobacterium leprae. 
The most common transmission is by direct interpersonal infection or mediated by insects, especially arthropods.
An incubation period (from 1-2 to 30 years) is followed by a period of invasion that is often associated with general symptoms, such as fever, headache, epistaxis, and neuralgic pains.
In a third time the characteristic manifestations of one of three forms appear: tuberculoid leprosy, lepromatous leprosy and mixed leprosy.
The tuberculoid leprosy is characterized by the appearance on the skin and viscera of nodules of various volume, isolated or confluent and that can be reabsorbed, thus leaving as aftermath white patches as atrophic or pigmented or ulcerated.
In lepromatous leprosy eruptions of bubbles (pemphigus leprosum), achromic anesthetic belmishes, gangrenes, areas of anesthesia “strip”, “boot” or “sleeve” anesthesia can appear. In the mixed leprosy can prevail one or the other form. Death occurs, after a course of variable length, for cachexia or kidney, lung, or other organs problems.
Dapsone is a sulfonamide used against leprosy since the Second World; it has a bacteriostatic action, due to its ability to substitute para-aminobenzoic acid (PABA), which becomes part of the structure of folic acid. Because of its replacement with the sulfonamide, the bacterial dihydropteroate synthetase, which is an enzyme present in bacteria and protozoa but absent in humans and that catalyzes the incorporation of PABA into the dehydrofolic acid, it can no longer synthesize the latter, with consequent stop of the bacterial multiplication.
Therefore, Dapsone acts as an antimetabolite, but it does not kill the bacteria, so that the patients were cured for all life long.
Combination chemotherapy (namely, the combined use of two or three drugs—Rifampicin, Clofazimine and Dapsone) continues to be the most important treatment of leprosy in the world; initial treatment lasted for periods varying from 1 to 3 years or more, but nowadays the duration of treatment has been reduced and varies from 6 to 12 months.
Dapsone is also used in the treatment of dermatological diseases; in this case, its pharmacodynamics has not yet been well understood. Certainly, it appears to have anti-inflammatory and immunomodulatory effects.
Dapsone is a compound of formula (I)
chemically known as 4,4′-diamino-diphenyl sulfone, described in FR 829 926 and marketed under the name of Aczone®.
FR 829.926 discloses a process for the synthesis of Dapsone, as reported in Scheme 1:
which is carried out in the presence of ammonia or an agent comprising ammonia or organic amines comprising at least one hydrogen atom bound to N, and wherein X is halogen.
U.S. Pat. No. 7,531,694 discloses a process for the synthesis of Dapsone, as reported in Scheme 2:

U.S. Pat. No. 6,998,490 discloses a process for the synthesis of Dapsone, as reported in Scheme 3:
